Paint materials with a multiplicity of different colour shades can be used in industrial painting systems, for example in the automobile industry, for the coating of workpieces such as automobile bodies. Depending upon the market segment of the manufacturer, this can be ten different colour shades, for example, or even fifty and more. Workpieces are usually painted by means of painting robots which are arranged in a climatized paint booth. The workpieces can be fed into the paint booth by means of a conveyor device where they are then coated by the painting robots. The order of the workpieces to be coated in a desired colour shade on the conveyor device is usually specified by the overall production process. A frequent colour change can therefore be implemented at the respective painting robots. For a cycle time of 60 s-80 s per workpiece or workpiece carrier, the number of colour changes called for can be several hundred per day and per robot.
With a colour changer according to the prior art, a multiplicity of paint material supply hoses opens out into a common manifold channel via appropriate valves. This is sealed at one end and, at its other end, has a fluidic connection to an atomiser by means of a hose connection. When a colour is changed, the paint material in the common manifold channel, hose connection and atomiser should first be pushed out as waste before this path can then be purged and new paint material subsequently pushed in.
When a colour is changed, in all cases it should be ensured that no paint is carried over. This is an introduction—even if only infinitesimally small—of a first paint material into a second paint material. Depending on the colour shades which are unintentionally mixed with one another, paint carryover can be highly detrimental to the painting result, for example when a small amount of a red colour shade finds its way into a white colour shade which then appears pink in some areas. To prevent paint carryover of this kind, it is essential to thoroughly clean the manifold channel appropriately when changing the colour.
However, paint carryover can occur in spite of appropriate cleaning measures, namely if one of the switching valves leaks, that is to say, in spite of an actually closed switching state, a quantity of paint material, albeit only small, finds its way from the respective supply line into the manifold channel. A known measure for further reducing the risk of paint carryover due to a leaking valve consists in fluidically connecting two valves or valve means in series to form a double arrangement and to switch them synchronously. In this case, leakage of the whole arrangement can be possible in the event of a defect in both of the series-connected valve means.
However, a series connection of valve means in a paint material switching path can increase reliability to a certain extent, as both valves are subject to the same switching cycles, and therefore synchronized wear and failure of both valves is probable.
Paint material switching paths according to known implementations can make detection of leakage of the valve means or allow detection from already incorrectly coated workpieces which are then scrap.